The Mach-US system is an OS developed as part of the CMU MACH project.
It is comprised of a set of servers, each of which supports
orthogonal system services. For example, instead of one server
supplying all of the system services as under the Mach BSD4.3 single
server (UX), the Mach Multiserver (Mach-US) has several servers: a task
server, a file server, a tty server, an authentication server,
a network server, etc. It also has and emulation library that is mapped
dynamically into each user process, and uses the system servers to support
the application programmers interface (API) of the UNIX operating system.

The Mach-US Architecture

Follow
this link
for a summary of the Mach Multiserver's main features.

If you have further questions about this work you may contact
J. Mark Stevenson at jms@cs.cmu.edu.

Mach-US: Research Rationale

Multiple system servers on a microkernel:
We wanted discover how
effective Multiple system servers on a Microkernel could be
in order to achieve better configability
and replaceablity of coherent subsystems of an OS implementation

Application Programmer Interface (API) neutral OS services :
We wished to determine if it is reasonable to
support multiple Application Programmer Interfaces,
like those of UNIX or OS2,
on the same standardized OS subsystems and interfaces.
Such standardized subsystems or interfaces are said to be
"API Neutral"

Remote Method Invocation (RMI) for OS services/objects
We wanted to evaluate object technology with Remote Method
Invocation for such a multi-server system

Client side OS computation:
to evaluate moving OS computation into the
client process to see how it might lower the load on the OS services

UNIX API re-implementation:
And to determine the feasibility of a UNIX implementation
in such an environment.

This paper describes requirements placed upon client-server interaction
in a multi-server operating system and how to answer those requirements.
Addressed are the problems of binding maintenance in the face of:
remote method invocation,
forking, binding transfer, authentication,
asynchronous interruption, and client crashes.

Emulation Services for Mach 3.0 Overview, Experiences and Current Status.